Several million pounds of olefin acid esters, particularly acrylate and methacrylate esters, are produced in industry each year for a wide range of applications including paint formulations, lenses, fiber optics, coatings, dental fillings and so forth. These industrial chemical intermediates have been prepared conventionally by Fischer esterification, wherein a mineral acid catalyst is employed. See, e.g., Mitsubishi Rayon Co. Ltd., Japanese patent 58,204,057 (1983). All references cited herein are incorporated by reference unless indicated otherwise. In the case where acrylate esters are prepared using the Fischer procedure, a danger of explosions exists due to rapid polymerization of the product. Another drawback of the Fischer procedure is that the procedure does not lend itself to reaction systems that contain acid-sensitive groups.
Other methods that are used to produce esters are generally based on the reaction of an acid chloride with an alcohol in the presence of a hydrochloric acid scavenger such as pyridine. See, e.g., MacCabe, J. F. and H. J. Wilson, J. of Oral Rehabilitation, 1:335 (1974); Sakaguchi, R. L., M. C. R. B. Peters, S. R. Nelson, W. H. Douglas and H. W. Poort, J. Dent., 20:178 (1992); and Kimura, H., F. Teraoka and T. Saito, J. Osaka Univ. Dent. Sch., 23:51-8 (1983). However, for the synthesis of acrylates, such methods require the use of acryloyl chloride or methacryloyl chloride which are lachrimators (irritating to skin, eyes, and mucous membranes), in addition to being toxic.
The reaction of an alcohol with an anhydride is yet another method of synthesizing esters. While methacrylic anhydride is commercially available, acrylic anhydride is not. Moreover, the preparation of acrylic anhydride, as in the case of most anhydrides, generally requires the reaction of the acrylic acid, or carboxylate ion of the acid, with acryloyl chloride. In an investigation concerning the polymerization of acrylic anhydrides, Hwa and coworkers synthesized acrylic anhydride, methacrylic anhydride, acrylic-methacrylic anhydride and acrylic-propionic anhydride by reaction of carboxylate salts with acryloyl chloride, methacryloyl chloride, acryloyl chloride and propionyl chloride respectively. Hwa, J. C. H., W. A. Fleming and L. Miller, Journal of Polymer Science: Part A, Vol. 2, pp. 2385-2400 (1964). In these syntheses, benzene was used as solvent and methylene anthrone (a polymerization inhibitor) was added. These investigators made similar, but unsuccessful, attempts to synthesize the following mixed anhydrides: methacrylic-isobutyric anhydride, dimethacrylic-fumaric anhydride, methacrylic-benzoic anhydride and methacrylic-cinnamic anhydride. In these reactions, the authors reported either symmetrical products, or mixtures of symmetrical and non-symmetrical products. Disadvantages of the above method include the health hazards associated with acryloyl chloride and benzene, which mitigate against its use in the synthesis of acrylic anhydride.